1. Field of the Invention
This invention relates to a fixing device that fixes an antenna portion on a mounting surface, and to an antenna device provided with the fixing device.
2. Description of the Related Arts
Heretofore, as an antenna device mounted onto an automobile roof and the like, the one capable of receiving a radio wave of multiple frequency bands used for Global Positioning System (GPS), satellite radio broadcasting, AM/FM radio broadcasting, telephone, television broadcasting and so on is generally known. The antenna device is fixed by an appropriate method after a fixing portion provided on the bottom surface thereof is inserted into a fixing hole (fixing opening) having a substantially square shape provided on a mounting surface of the automobile roof and the like.
An antenna holder is known, for fixing and mounting an antenna base of the antenna device on the automobile roof, which includes: an anchor claw having four arms curved into an S-shape; a spreading element for spreading the arms; a screw (bolt); and a socket portion attached to the antenna base (refer to Japanese Patent Application Laid-Open Publication (Translation of PCT Application) No. 2009-528487). The anchor claw and the spreading element respectively have penetration openings. The antenna holder is set to an initial state before deformation of the arms when the screw penetrates the penetration openings and is tightened halfway on the antenna base.
The socket portion has a shape to contact the inner side of the fixing opening of the automobile roof. In the initial state, the anchor claw, the spreading element, the screw and the socket portion are configured to become smaller in area than the fixing opening. The anchor claw, the spreading element and the screw in the initial state of the antenna holder are penetrated through the fixing opening, the socket portion is fitted in the fixing opening, and the screw is tightened further. By this, the four arms of the anchor claw spread and are bent while being deformed. The plural bent arms and the antenna base clamp the automobile roof, thereby fixing the antenna holder on the automobile roof.
Furthermore, an antenna holder in which arms do not deform is known (refer to International Publication No. 2009-143905). The antenna holder includes: a supporting portion having four L-shaped arms which do not deform; a screw (bolt); rotation inhibiting portions for the screw; and four guide portions attached to the antenna base. The supporting portion and rotation inhibiting portion for the screw respectively have penetration openings. The screw penetrates the penetration openings and is tightened halfway on the antenna base to set the antenna holder to an initial fixed state in which positions of the arms are fixed with respect to the antenna base. The rotation inhibiting portions are members that restrict the rotation of the supporting portion in association with rotation of the screw. Also, the rotation inhibiting portions are structured to lock a rotation position of the supporting portion in the initial fixed state.
The guide portions are provided at positions that contact the inner side of the fixing opening of the automobile roof. In the initial fixed state, the arms of the supporting portion are configured to be respectively positioned on diagonal lines of the fixing opening so that the area including the supporting portion, the rotation inhibiting portions and the screw become smaller than the area surrounded by the guide portions (fixing opening). The supporting portion, the border fixing portion and the screw in the initial state of the antenna holder are penetrated through the fixing opening, the guide portions are fitted in the fixing opening, the supporting portion is rotated to position the arms thereof at the center lines of four sides of the fixing opening, and the screw is tightened further. By this, the four arms moves towards the antenna base, and the four arms and the antenna base clamp the automobile roof and fix the antenna holder onto the automobile roof.
However, in the conventional antenna holder with arms which do not deform, the upper ends of the guide portions are positioned lower than the lower ends of the arms in the vertical direction of the roof in the initial fixed state. This allows the arms to be easily affected by impact from the outside. The impact may cause a risk of the arms being projected out of the region surrounded by the guide portions when the arms rotate and disconnect the locking state and releases the initial fixed state.
The impact from outside includes vibration of the antenna holder while being transported and external force applied by an operator while the antenna being mounted onto the automobile roof. When the initial fixed state is released, the assembly operator needs to reset the antenna holder to the initial fixed state before mounting the antenna holder onto the automobile roof through the fixing opening. This may cause a complication in the operation.
Furthermore, when attaching the antenna holder onto the fixing opening, the attaching operation may become difficult as a periphery of the fixing opening get caught between the arms and the guide portions, causing the position of the antenna holder to become shifted with respect to the fixing opening.